Of particular concern after TBI are adverse outcomes that affect health and the ability to function in society. The Institute of Medicine (2009) Committee on Gulf War and Health recently conducted a large-scale and detailed systematic review of the literature to answer the question, "What are the long-term outcomes associated with sustaining TBI?" The committee reported significant limitations in many of the existing studies, including reliance on self-report, small sample sizes, lack of uniformity in defining TBI severity, and inadequate comparison groups. However, they also found evidence in the literature of a range of adverse long-term health outcomes (lasting greater than 6 months) associated with moderate and severe TBI and mild TBI with LOC. The committee's main findings for the studies that could be categorized by TBI severity are summarized in Table 1–5. According to the committee, evidence of long-term adverse health effects was strongest for moderate, severe, and penetrating TBI and limited or inadequate for concussion/mTBI. The evidence of an association between concussion/mTBI alone and long-term neurocognitive deficits (defined as performance on tests of sensory integrity, motor speed and coordination, attention, processing, and executive functions) was found to be insufficient/inadequate based on the published literature to date. The committee also found insufficient/inadequate evidence for the association between concussion/mTBI and long-term social and occupational dysfunction. Although they concluded on the basis of combined results from studies of a range of TBI severity that there is sufficient evidence of an association between sustaining a TBI and development of postconcussive symptoms (such as memory problems, dizziness, and irritability), this finding is problematic. Specifically, there was no adequate evaluation of the association of concussion/mTBI alone with postconcussive symptoms because in some studies, data were not analyzed separately for concussion/mTBI and moderate/severe TBI, or postconcussion-symptom inventories were used to assess symptoms in persons who had moderate to severe TBI. The failure to separate concussion/mTBI from moderate/severe TBI in the evaluation of postconcussive symptoms is a problem in some natural history studies of TBI.